Maybe to your disappointment it is not about
video(*). The scope of this page is primarily
computer storage applications of DVD±RW/±R,
things like backup, archiving, data exchange... The
downloadable files are an optionalLinux 2.4 kernel DVD+RW patch and a
couple of user-land utilities dubbed as dvd+rw-tools.
Though it doesn't mean that you can't burn
DVD-Video discs with dvd+rw-tools. [Unlike Video-CD] DVD-Video
is "molded" in an ordinary data file system and
therefore no explicit support by the burning program is
actually required. In other words it is the DVD-Video
content preparation which is beyond the scope of this
Kernel patch? This sounds too complicated
already! Can't I just use cdrecord?
It should be explicitly noted that the user-land
utilities, dvd+rw-tools, do suffice for DVD recording
without explicit kernel support. So if they fulfill your requirements, thenpatching the kernel is by all means optional. As
for cdrecord, DVD+RW/+R recording strategies are somewhat
different from the one supported by cdrecord, so it simply
doesn't work (nor does dvdrecord, despite
7.3 Release Notes say).
What is the kernel patch good for then?
DVD+RW (but not DVD+R) is a true random write access media
and therefore is suitable for housing of an arbitrary file
system, e.g. udf, vfat, ext2, etc. This, and this alone,
qualifies DVD+RW support for kernel implementation.
However, I have to recommend to deploy it with
caution, see tutorial for further
details. Also note that not all OEMs seem to live up to the
promise of true random write access. As for the moment of this
writing apparenly only 2nd generation Ricoh-based units (see dvdplusrw.org for
generation listings) equipped with later firmware can sustain
I/O fragmentation (see Technical Ramblings below for further
details) and perform reliably.
What are the dvd+rw-tools for?
As implied/already mentioned - to master the DVD media,
both +RW/+R and -R[W]. I could simply
refer to the tutorial below, but figured that couple of words
about the [original] design ideas behind growisofs, the
principal burning utility, wouldn't harm. Even though a
modified kernel can let you put for example an ext2 file system
on DVD+RW, it's probably not very practical, because you most
likely want to access the data on an arbitrary computer.
Or in other words you most likely want ISO9660. The trouble is
that you might as well want to add data now and then.
And what options do you have in the lack of multiple sessions
(no, DVD+RW has no notion of multiple sessions)? Complete
re-mastering which takes more and more time as data set grows?
Well, yes, unless you employ growisofs! Growisofs
provides the way to both lay down and grow an ISO9660
file system on (as well as to burn an arbitrary pre-mastered
image to) all supported DVD media.
But if they support both + and - recording
strategies, why are they called dvd+rw-tools?
For historical/nostalgical reasons, as originally they did
support exclusively DVD+plus. On the other hand now, when the
vast majority of DVD burners that are being introduced to the
market today are DVD+capable, the name most likely refers to
your unit in either case. And you can always consider the plus
in the name as notion of some unique quality, such as
"seamless" multi-sessioning, not as reference to some
Yes. It should be explicitly noted that growisofs is a
front-end to mkisofs, i.e. invokes mkisofs to perform the
actual ISO9660 file system layout. Secondly, the DVD burners
available on the market can burn even CD-R[W] media and
cdrecord is the tool for this job [and this job only].
Does it work with my DVD burner?
If your unit is MMC complaint,
then the answer is "most likely it
just does." Well, as the probability of your unit being
non-MMC complaint is virtually zero, the answer in practice is
unconditionally "most likely."
The [core] tools were reported to work with a wide range of
drives, including [but not limited to] HP
ND-100,TDK indiDVD 4x0N,Plextor PX-0x,Benq DW00A,OptoRite DD020x,Lite-On LDW-x1S,
as well as nonplus units such as
G[MS]A-400,Panasonic UJ-811 and
Is there a GUI front-end available for
K3b, version 0.10
and later, and nautilus-cd-burner,
version 0.5.1 and later, are both hiding growisofs behind their
pretty buttons and menus:-) Keep in mind that those are not
directly related to dvd+rw-tools development
effort and GUI users should turn elsewhere for end-user
support. Oh! dvd+rw-tools 5.10.x is a minimum requirement for
I don't run Linux. What are my options?
Version 5.4 adds support for OpenBSD/NetBSD.
Version 5.6 adds support for Solaris 2.x [commercial licensing
terms for distribution on Solaris are to be settled with Inserve Technology].
Version 5.8 features FreeBSD port(*)
contributed by Matthew Dillon, FreeBSD Development Team
alumnus. Hewlett-Packard Company has donated
HP-UX 11 support for
5.14(**). Whenever separately available [and unless
stated otherwise], use character-type device entry with
dvd+rw-tools, e.g. OpenBSD/NetBSD users should
stick to /dev/rcdXc.
FreeBSD tip! If you have an IDE unit, atapicam
is your mantra! Secondly, if you have devfs mounted,
you might have to mountfdescfs as well.
As of 5.14 HP-UX support is classified as
"initial," do provide feedback!
Given the absolute lack of initial support from
vendor(s) dvd+rw-tools arose from guesswork. There still is a couple
of fatal failures indicated by vendor-specific error codes (see
Technical Ramblings) and I haven't yet figured out the way around
them in kernel. User-land utilities are considered stable enough to be
deployed in "production environment."
As of May 2003 I've decided to advise users to
turn to <email@example.com>
on support matters. It's an open list, meaning that you don't have
to be subscribed to post
a problem report. List archives can be found at both subscribe page and mail-archive.com.
When submitting report, provide version information, exact command
line(s) and exact output generated by the program, do complement
it with dvd+rw-mediainfo output for resulting recording.
Do check couple of last archived months, as the
issue might have been discussed recently. If you've chosen to
contact me personally and haven't heard back within a week or so, then
you most likely overlooked something on this page. Please read it more
Special thanks for hardware donations [in
If your burner unit is under some kind of
removable media automounter control, such as autofs, supermount,
magicdev or similar, take it out of its control! I can't help
you with the latter, check your system documentation (such as google:-)
for specific instructions. Failure to take your
unit out of automounter control can result in busted recording, a
coaster! At the very least you have to make sure your unit
is not automouted during recordings.
If you have an IDE unit and run 2.4.x
kernel, you most likely want to "route" it through ide-scsi
emulation layer by either:
argument to kernel;
appending following lines to your /etc/modules.conf:
Keep in mind that once hdX
is routed through ide-scsi, you can no longer refer to /dev/hdX(*), but to corresponding
well, except as in hdparm -d [0|1] /dev/hdX. As for DMA settings. Several users of
NEC[-based] units have reported that their systems crash during DVD
recording. The problem appears to be related to DMA settings, at least
switching it off reportedly helps. The problem might be specific to
some IDE chipsets...
If you have an external unit, just get
it working as CD-ROM first. I myself have no personal experience
whatsoever with USB or IEEE1394/Firewire storage devices
of any kind and have to direct you elsewhere for specific instructions.
I however am confident that if you manage to get your drive working
reliably as CD-ROM and CD-R[W] burner, then you won't
have any troubles with DVD recording part. USB connected drives were
reported to be working fine since eternity. Firewire connected drives
in turn were reported to fail miserably under 2.4.18. The failure
didn't seem to be DVD+RW related as it reportedly failed burning even
CD-R media. Firewire support was substantially revamped in 2.4.19, and
dvd+rw-tools were reported to work with this and later kernels.
If you're running 2.4.19 or .20, consider
applying this drivers/scsi/sg.c patch.
The bug is fixed in .21. I write "consider" and not
"do" for the following reasons:
dvd+rw-tools are not affected by this bug (as they don't use SG_IO
interface), cdrecord [potentially] is;
I however haven't actually experienced the problem with cdrecord
(maybe yet, kernel could have managed to keep buffers neatly aligned
while talking to cdrecord those times I tried), it was VMware that has
failed miserably on me;
As of version 5.6 dvd+rw-tools add support for SG_IO
pass-through or in other words support for Linux 2>=5[.43].
Even though the sg bug is present even there, e.g. in 2.5.69, fixed in 2.5.71, dvd+rw-tools are
still not affected by it. As for 2>=5 in more general sense. As you
might know "the[ir] official plan™" is to scrap
ide-scsi.c. The idea is to bypass the real SCSI layer and get SG_IO
working against /dev/hdX directly.
Not that I'm fond of the idea, yet I wish it worked without need for interim
patches #1 and #2, (the latter is relative to
2.5.69-75, the 1st problem is addressed in .71, 2nd one - .75-bk3 in
minute" prior first 2.6 cut:-).
Download, unpack and compile the the tool-chain. To build the thing do pick the
.tar.gz archive, which contains Makefile as well as .spec file. You
will need both C and C++ compilers installed. Separate
source code files found in the download catalog
are provided mainly for on-line reference purposes (such as revision history:-).
If your Linux kernel supports multiple ABIs (e.g.
Linux-sparc64 can run even 32-bit Linux-sparc applications, as well as
Linux-x86_64 can execute legacy 32-bit i386 binaries), make sure you
compile for native 64-bit ABI (which can normally be done with
'make TARGET_ARCH=-m64'). The problem here is that 64-bit
kernel has to explicitly convert ioctl structures passed by 32-bit
applications and apparently it does really lousy job when it comes to
CDROM_SEND_PACKET ioctl deployed by dvd+rw-tools.
If you have 1st generation drive (Ricoh
MP5120A and derivatives, see dvdplusrw.org for generation
listings), do consider upgrading your firmware (see Ricoh
page for latest version information). Fixed bug descriptions are vague,
but at the very least after upgrade to 1.34 I could no longer reproduce
infrequent "random positioning errors" when reading a
file system with a lot of small files. 1.34 adds support for Verbatim
media and 1.37 apparently for Memorex. Version 1.37 also implements a
secret vendor-specific command which reportedly
improves compatibility with a number of DVD-ROM drives (more about
this matter in Technical Ramblings).
Several 2nd generation unit (Ricoh
MP5125A and derivatives) users have reported that their systems
lock up the while recording DVD+R, but not DVD+RW. I myself have never
experienced anything similar, but firmware upgrade did help those who
has suffered from this. So that apparently even 2nd generation users
should be considering firmware upgrade. Firmware upgrade is actually
required if you want to burn 4x media in your 2nd generation unit.
Well, it will still burn it at 2.4x, but without firmware upgrade you
should expect deplorable results.
Well, as new media brands and new products are being
introduced to the market all the time, it apparently pays off to
periodically check for firmware updates. It's not as simple as
"1st" vs. "2nd generation" units anymore, so turn
to your vendor to be sure. Special note for HP users. HP no longer
posts firmware updates on the web-page. Instead they let some Windows
auto-update gizmo to pick firmware updates among
dvd[1-4]00*.exe files in their FTP
directory, so that readers of this page tend to miss them...
Formatting the DVD+RW media. Virgin
DVD+RW media needs to be initally formatted prior usage. Once again,
only virgin DVD+RW media needs to be formatted. As of version
5.10 growisofs detects blanks and applies initial formatting procedure
automatically. Otherwise same effect can be achieved by passing the
device name, e.g. /dev/scd0, as an argument to dvd+rw-format. To make formatting
process reasonably fast, less than 1 minute, the media gets formatted
only partially, as you can notice by observing a progress indicator
displayed by dvd+rw-format. The final indicator value varies from
firmware to firmware, values as low as 1.6% were observed. But it does
not mean that you can only write that little. The unit keeps formatting
transparently, as you add more data. Oh! Do keep in mind that
DVD capacity of 4.7GB are salesman's GB, i.e. 10003 and
It was observed that excessive reformats can render
media unusable already after 10-20 reformats. It appears to be a
firmware deficiency, not some common media defect [at least it was
perfectly possible to salvage the media in a unit of different brand],
but I don't recommend [enforced] reformat in either case. Note that
DVD+RW re-formatting procedure does not substitute for blanking.
If you want to nullify the media, e.g. for privacy reasons, do it
explicitly with 'growisofs -Z /dev/scdN=/dev/zero'. Otherwise just write over
previous recording as it simply wasn't there, no re-formatting is
DVD+R media does not require any formatting
procedure applied and is ready to use out-of-the-box. Apparently, a
reminder that 1st generation units (Ricoh MP5120A and derivatives)
are not capable of burning DVD+R is needed.
Burning with growisofs. There is hardly a need for
manual for growisofs. In a nutshell growisofs just passes all command
line arguments to mkisofs and dumps its output directly onto the media.
The first part means that you basically can [well, should]
consult mkisofs manual page and
accompanying reference documentation (including multi-session related
section[s]) and the second part means that you shouldn't expect an
ISO-image on the standard output (nor make sure you have enough free
temporary storage:-). Differences from mkisofs command line
you may not use -o option;
you don't have to specify -C option, growisofs will construct one
there is internal -Z option for initial session recording, this
substitutes for originally suggested 'mkisofs | dd of=/dev/scd0';
Otherwise everything that applies to
[multi-session] mastering with mkisofs applies to growisofs as well. For
example just like with mkisofs you should make a note on which options
you used to master the initial "session" with and stick to
Oh! Do make sure you have at least mkisofs 1.14 on your $PATH (mkisofs 1.14 is part of cdrtools
1.10). If you consider passing /same/files as argument, or in
other words consider deploying growisofs for incremental
multi-session backups, then you shall find this '-old-root' extension to
mkisofs 2.0-2.01 simply indispensable.
The idea and implementation by Patrick Ohly is to
"graft" recording sessions as separate directories. Each
backup increment/directory is ment to contain both updated files and
references to previously backed up ones, which facilitates
comparison between increments as well as fine-graded restore.
In addition to intuitive -Z interpretation,
growisofs [version 3.3 and later] recognizes special form of -Z command
line option which permits burning of arbitrary pre-mastered images. The
"magic" command is:
growisofs -Z /dev/scd0=image.iso
where image.iso represents an arbitrary
object in the file system, such as file, named pipe or device
entry. No, nothing is "growing" here and command name is
counter-intuitive in this particular context. And here is even less
intuitive:-) If you wish to burn down output generated by an
arbitrary program, you can use:
dumpsomething | growisofs -Z /dev/scd0=/dev/fd/0
Burning DVD±R implies extra limitations:
Needless to say that you have only one shot with -Z
Unlike DVD+RW, DVD±R media does have notion of multiple
sessions. However! Not all legacy units can "see"
beyond the first one. Few DVD-ROM units are capable of DVD-R
multi-border playback, even fewer support DVD+R multi-sessioning. In
other words your DVD burner might be the only unit in your vicinity
capable to access data added at different occasions.
Even if your DVD unit does "sense" multiple sessions,
Linux kernel sometimes fails to pull that information from the
drive:-( Till the problem is looked into and resolved you can
work it around by reloading corresponding driver, most likely
And once again, do keep in mind that 4.7GB are
salesman's GB, i.e. 10003 and not 10243. If
translated to "real" GB, DVD±R[W]
capacity is not larger than 4.4GB! It should also be noted that earlier
growisofs versions did not check if there is enough space on media to
accommodate the data set to be burned, meaning that it was your sole
responsibility to make sure "overburn" condition is not
raised. As of version 5.2 growisofs performs the necessary checks
for you and refuses to start recording if "overburn"
condition appears to be unavoidable. This behaviour can be overridden
with -overburn command-line option.
If you're satisfied with growisofs, then you
should just proceed to the next chapter
and abstain from applying the optional 2.4.x kernel patch. If
you haven't stopped reading beyond this line, download the patch, apply it, rebuild the
kernel or modules and re-install (kernel or cdrom.o and sr_mod.o
modules, whichever appropriate), but don't ask mehow. As you could
have noticed, patch targets SCSI CD-ROM module. This means that you
have to "route" your IDE unit through ide-scsi to get this one
working. To see it in action, insert formatted DVD+RW media and try to
access it, 'dd if=/dev/scdN count=0'
would do. Then verify that kernel logs "srN: mmc-3 profile: 1Ah". You should now be
able to 'mkisofs -pad . | dd of=/dev/scdN
obs=32k' or even 'mke2fs -b 2048 /dev/scdN' and observe kernel logging "srN: dirty DVD+RW media."
Linux 2.6 DVD+RW kernel support is planned in
line with DVD+MRW kernel support. This [unfortunately] means that
industry has to deliver a DVD+MRW capable unit first. Yes, the last
sentence means that despite all the promises, there are no such units
available on the market yet. As of the 1st of August 2003, Ricoh MP5240A,
Philips DVDRW416K or BenQ DW400A do not actually implement
Mt.Rainier/EasyWrite support. It remains to be seen if they will offer
it in form of firmware upgrade. In either case, the [original] project
goal is not only read-write support for DVD+[M]RW capable units
themselves, but even playback of DVD+MRW formatted media in legacy
DVD-ROM units (when defect list will be read and interpreted by OS
software in opposite to Mt.Rainier firmware).
Even though kernel now
permits to build and mount arbitrary file system, there is one thing you
must keep in mind before you just proceed, no matter how
tempting it might appear.
As you might know DVD+RW media can sustain only
around 1000 overwrites. The thing about fully fledged file systems
is that every read [or tight bunch of 'em] is accompanied by
corresponding i-node update or in other words a write! Now, let's say
you lookup the mount point (e.g. ls /mnt/dvd) ten times a day. This
gives you a 100 days lifetime on your mountpoint and therefore media.
Not really much, huh? So do use noatime mount option with
DVD+RW media or have it mounted read-only most of the time. However!
Every read-write mount "costs" a super-block update. So that
if you remount the media say 3 times a day, it would last for about a
would exhaust the "budget" way sooner]... Defect management
[in firmware, a.k.a. Mt.Rainier,
or at file system level] would improve the situation, but ideally
file system driver should definitely refrain from modifying the
super-block [marking it dirty] if nothing was actually written since
last mount. Given the development status of Linux UDF the
chances for seeing the latter implemented [for UDF] are more than just
conceivable. The request is already filed and even possible solution is
being discussed. But why not give UDF a shot already then? By default
UDF write support is unfortunately disabled and you might have to
reconfigure the kernel and rebuild modules. Alternatively [my preferred
option actually] fetch the code at SourceForge and
build the module separately. Of course you will have to fetch and build
udftools as well. But once it's done just type:
mkudffs --spartable=2 --media-type=cdrw /dev/scdN
mount -o rw,noatime /dev/scdN /mnt/cdrom
mkudffs command line options were suggested
by UDF maintainer, Ben Fennema.
Performance optimization. This paragraph
applies only if you've patched the kernel. As some of you might
remember the original recommendation was "do use obs=32k
for optimal performance." Well, it was rather naive of me to say
so, as common block device layer completely reorganizes the
stream so that '>/dev/scd0' is as good as '|dd
of=/dev/scd0 obs=32k'. It should also be noted that dumping to
/dev/scd0 puts quite a pressure on VM subsystem, as the data passes
through block buffer cache. To minimize the pressure and improve
overall system performance bind the cdrom device to a raw device, e.g.
'raw /dev/raw/raw1 /dev/scd0', growisofs will locate and use
it automatically. obs=32k makes perfect sense with /dev/raw devices,
but dd (as well as most other programs, e.g. tar) won't work as
/dev/raw expects specifically aligned buffer... As temporary
workaround, just to get you going so that you can start figuring things
out, consider this
Compatibility: caveat lector
This paragraph discusses "DVD-ROM
compatibility," or playability of already recorded media in legacy
units. Blank media compatibility issues, or cases such as failure to
start or fulfill recording because of poor media support by burner
firmware, are beyond the current scope. Turn to your vendor for list of
supported media and/or to the public to share your
In order to optimize seek times DVD[-ROM] players
calibrate their mechanics every time the media is loaded by sliding
the optical head some place, picking up the signal and noting the
physical block address underneath the lens. In order for this procedure
to work with re-writable/recordable media, that particular spot has to
be written to [or de-iced in DVD+RW case]. Some units slide the head to
30mm [radial] to calibrate, some to 35mm. In order to keep such players
"happy," make sure that at least 1GB is written [before you
attempt to mount it in DVD-ROM unit].
Other units attempt to seek to lead-out [or vicinity
of it] for calibration purposes. Now the catch is that it's perfectly
possible to produce a DVD+RW disc without lead-out. Most notably media
initially formatted with dvd+rw-format [apparently] doesn't have any
lead-out, not to mention that practically whole surface remains virgin.
If you fail to mount/play DVD+RW media, attempt to
dvd+rw-format -lead-out /dev/scdN
which relocates the lead-out next to outermost
written sector as well as makes sure there is no virgin surface before
it. Previously written data is not affected by this operation.
Then non-finalized DVD+R and Sequential DVD-R[W]
discs don't have lead-out either(*). If you fail to
mount/play DVD+R media and wish to sacrifice the remaining space for
immediate compatibility, just fill the media up(**).
Alternatively if you master volume in a single take and don't plan to
use it for multi-sessioning(***), you have the option to
invoke growisofs with -dvd-compat option and cut the real
lead-out directly after the first session.
Well, there are lead-outs at the session edges, but
the problem is that "End Physical Sector Number of Data Area"
field in "Control Data Zone" of the lead-in contains address
of the largest media sector, which makes affected DVD[-ROM] players
calibrate at the outermost edge instead of the first session. Actually
I fail to understand why don't they burn the address of last sector of
the first session in the lead-in even on multi-session discs...
But beware the 4GB limit!
If 4GB is already an issue, or if you don't feel like throwing
unrelated data on the media in question, then invoke 'growisofs
-M /dev/scd0=/dev/zero' (supported by 5.6 and later).
Alternative is to re-master the whole volume, naturally with
E.g. when mastering DVD-Video disc:-) Note that
-dvd-video option [passed to mkisofs] engages
Then we have logical format compatibility
issue(s). Probably the very ground for all the controversy around
DVD+RW, rather around DVD+RW media not being playable in a whole range
of players. DVD+RW Alliance was keen to blame on DVD-ROM vendors, even
claiming that they deliberately block playback. But the fact is that
format specifications don't explicitly say that unrecognized format
[designated by "Book Type" field in "Control Data
Zone" of the lead-in] should be treated as DVD-ROM and [in my
opinion] it was rather naive of them to claim and expect that the media
will be playable in "virtually all players." This deficiency
was recognized by practically all DVD+RW vendors [well, apparently by
"traditional" DVD+RW vendors and not "latest
generation" vendors such as Sony, NEC, TDK...] and a secret vendor-specific command
manipulating this "Book Type" field was implemented. So if
you fail to mount/play DVD+RW media, you might have an option to
dvd+rw-booktype -dvd-rom -media /dev/scdN
Once again. Not all vendors support this and you
can't expect this utility to work with all recorders.
It's naturally not possible to manipulate the
"Book Type" field on DVD+R media, that is not after the
lead-in is written [which takes place at the moment the first session
gets closed]. But it might be possible to control how it [lead-in] is
going to be branded by programming the drive in advance:
There [potentially] are other logical
DVD+RW(*) format incompatibilities, but the "Book
Type" issue discussed above is the only one "officially"
recognized. Well, it's actually understandable as it's the only one
that can be recognized and addressed by a DVD+RW vendor alone.
Recognition of other incompatibilities would require cooperation from
DVD[-ROM] player vendors and that's something they apparently are not
willing to show referring to the fact that DVD+RW format is not
approved [and apparently never will be] by DVD Forum(**).
Finalized DVD+R media branded with DVD-ROM
"Book Type" is virtually identical to DVD-ROM.
To which I say "so what?" DVD Forum is an
alliance of manufacturers just like DVD+RW Alliance is. It [or any
other party for that matter] has no authority to deny a technology
Finally there is a physical incompatibility issue.
They claim that there are optical pick-ups out there not being capable
to decode the track because of low reflectivity of DVD+RW media
surface. I write "they claim," because in the lack of
cooperation from DVD[-ROM] vendors it's not possible to distinguish
physical from logical format incompatibility, which I find important to
tell apart in order to make sure at least logical format
incompatibility issues don't persist over time. It might be as trivial
as following. As you surely know [already], DVD+RW has same
reflectivity as dual-layer DVD-ROM. Now the catch is that the linear
pit density in turn is same as of single-layer one. Meaning that if
player makes assumptions about linear pit density based on
reflectivity, then it won't be able to trace the track... But either
way, there is very little you can do about this one, but to try another
As for multi-session ISO9660 [DVD]
recordings! Unfortunately, Linux ISOFS implementation has certain
deficiency which limits interoperability of such recordings. In order
to understand it, have a look at sample ISO9660 layout to the right...
Now, the problem is that isofs i-nodes(*) are 32 bits wide
(on a 32-bit Linux) and represent offsets of corresponding directory
entries (light-greens), byte offsets from the beginning of media. This
means that no directory (green areas) may cross 4GB boundary without
being effectively corrupted:-( It should be noted that in
reality it's a bit better than it looks on the picture, as mkisofs
collects all the directories in the beginning of any particular session
(there normally are no blues between greens). The first session
is therefore never subject to i-node wrap-around, but not the
subsequent ones! Once again, files
themselves may reside beyond the 4GB
boundary, but not the directories, in
particular not in further sessions. Having noted that directory entries
are actually specified to start at even offsets, I figured that
it's perfectly possible to
"stretch" the limit to 8GB. But in order to assure the
maximum interoperability, you should not let any session
start past 4GB minus space required for directory
structures, e.g. if the last session is to fill the media up, it
has to be >400MB. As of version 5.3 growisofs refuses to append
a new session beyond 4GB-40MB limit, where 40MB is pretty much
arbitrary chosen large value, large for directory catalogs that is. Yet
it doesn't actually guarantee that you can't suffer from i-node
wrap-around. The fs/isofs kernel patch is
addressed to those who have actually ran into the problem and have to
salvage the data.
i-node is a number uniquely identifying a single
file in a file system
Why media reload is performed after every
recording with growisofs? Well, it's performed only if you didn't
patch the kernel:-) But no, I'm not insisting on patching the kernel!
All I'm saying is that in the lack of kernel support, media reload is
performed for the following reason. In order to optimize file access
kernel maintains so called block cache, so that repetitive requests for
same data are met directly from memory and don't result in multiple
physical I/O. Now the catch is that block cache layer remains totally
unaware of growisofs activities, growisofs bypasses the block
cache. This means that block cache inevitably becomes out of sync,
which in turn might appear to you as corrupted data. Media reload is
performed to flush/resync the block cache.
What does [kernel] "DVD+RW support"
really mean? Even though DVD+RW has no notion of [multiple]
sessions, to ensure compatibility with DVD-ROM it's essential to issue
"CLOSE TRACK/SESSION (5Bh)" MMC command to
terminate/suspend background formatting (if any in progress) whenever
you intend to eject the media or simply stop writing and want better
read performance (e.g. remount file system read-only). This is what the
patch is basically about: noting when/if media was written to and
"finalizing" at unlock door.
Secondly, whenever you employ fully fledged
file system, I/O requests get inevitably fragmented.
"Fragmented" means following. Even though you can address the
data with 2KB granularity, it [data] is physically laid out in 32KB
chunks. This in turn means that for example writing of 2KB block
involves reading of 32KB chunk, replacing corresponding 2KB and writing
down of modified 32KB chunk. "Fragmented requests" are those
that are smaller than 32KB or/and cross the modulus 32KB boundaries. In
order to optimize the process certain caching algorithm is implemented
in unit's firmware. Obviously it can't adequately meet all possible
situations. And so in such unfortunate situations the drive apparently
stops processing I/O requests returning "COMMAND SEQUENCE ERROR
(2Ch)" ASC. This is the second essential of "DVD+RW
support," namely injecting of "SYNCHRONIZE CACHE (35h)"
MMC command in reply to the error condition in question. The command
flushes the cached buffers which makes it possible to resume the data
Unfortunately the above paragraph doesn't
seem to apply to the 1st generation drives, Ricoh MP5120A and
derivatives:-( "SYNCHRONIZE CACHE (35h)" doesn't
seem to be sufficient and the unit keeps replying with "COMMAND
SEQUENCE ERROR (2Ch)" going into end-less loop. This makes it
impossible to deploy arbitrary file system. I'm open for
suggestions... Meanwhile the I've chosen to simply suspend I/O till the
media is unmounted.
Even 2nd gen unit were reported to exhibit similar
[but not the same] behaviour under apparently extremely rare
circumstances. At least I failed to reproduce the problem... The problem
reportedly disappears with firmware upgrade...
This one really beats me. Sometimes the unit
simply stops writing signaling a vendor specific positioning error,
03h/15h/82h to be specific. Especially if the media is newly formatted.
Couple of work theories. One is that block buffer cache reorders
requests so that they are not sequential anymore, "FLUSH
CACHE" might do the trick. Another one is that under
"underrun" condition background formatting kicks off and has
to be explicitly stopped. "Underrun" is in quotes because
the unit is supposed to handle temporary data stream outages
gracefully. If you run into this (you most likely will), try to
complement growisofs command line with [undocumented]
-poor-man option (which has to be first in the command line).
This option eliminates request reorders and minimizes possibility for
"underrun" condition (by releasing the pressure off VM
The original idea was to implement DVD+RW support in
drivers/cdrom/cdrom.c. Unfortunately SCSI layer maintains private
"writeable" flag controlling the ability to issue WRITE
commands. The flag is impossible to reach for from the Unified CD-ROM
driver. But why am I talking about SCSI when there are only IDE units
out there (at least for the time being)? Well, as you most likely want
to occasionally burn even CD-R[W] with cdrecord you want it to go
through ide-scsi emulation layer anyway. So I figured that SCSI CD-ROM
driver is the one to aim for even for DVD+RW.
Unfortunately it was not possible to implement it
completely in sr_mod.o:-( Minor drivers/cdrom/cdrom.c
modification was required to sense the media before decision about
whether or not to permit write open. That's because DVD+RW drives are
morphing their behaviour after currently mounted media and it's
essential to identify newly inserted media.
Special comment about "what a dirty
hack!!!" To my great surprise it turned out that time-out value you
pass in cdrom_generic_command is simply ignored and time-out is set to
pre-compiled value of 30 seconds. Unfortunately it's way too low for
formatting purposes and I had to do something about it. Alternative to
"the dirty hack" was to add another argument to sr_do_ioctl
and modify all the calls to it... I've chosen to take over those 31
unused bits from the "quiet" argument instead of modifying
all the calls (too boring).
But even if time-out value passed down to kernel
(with either CDROM_SEND_PACKET or SG_IO ioctl) is taken into
consideration, it's apparently not interpreted as user-land code
expects it to. As I figured... There is no documentation on
CDROM_SEND_PACKET, but following the common sense most programmers
(including myself:-) expect it to be interpreted in at least
platform-independent manner, such as milliseconds maybe? SG_IO timeout
in turn is documented
to be measured in milliseconds... Neither of this holds true! Kernel
treats these values as "jiffies," which is a
platform-dependent value representing time elapsed between timer
interrupts. But if we attempt to send down "jiffies," it
might turn out wrong too [at least for the moment of this writing]. The
catch is that [IA-32] kernel developers figured it's cool to shorten
"jiffy," but didn't care to provide user-land with actual
value (well, not of actual interest, too much legacy code to deal with)
accordingly in respect to the legacy value of 10ms.
There is another kernel "deficiency" I ran
into while working on the (original version of) dvd+rw-format utility.
The drive provides background formatting progress status, but
unfortunately it's impossible to access it. That's because progress
counter is returned [in reply to "TEST UNIT READY"] as
"NO SENSE/LOGICAL UNIT NOT READY/FORMAT IN PROGRESS" sense
bytes but with "GOOD" status. Apparently any sense data with
"GOOD" status is discarded by the common SCSI layer.
What does plus in DVD+RW/+R
stand for? Originally this paragraph started as following:
The key feature of DVD+RW/+R media is
high [spatial] frequency wobbled [pre-]groove with addressing
information modulated into it. This makes it possible to resume
interrupted [or deliberately suspended] burning process with accuracy
high enough for DVD[-ROM] player not to "notice" anything at
playback time. Recovery from buffer underrun condition in DVD-RW/-R
case in turn is way less accurate procedure, and the problem is that
the provided accuracy is very much what average player can tolerate.
Now given that both provided and tolerated inaccuracies are
proportional to respectively writing and reading velocities there
basically no guarantee that DVD-RW/-R recording that suffered from
buffer underrun will be universally playable.
Well, it turned out that I was wrong about one
thing. I failed to recognize that DVD-R[W]
groove also provides for adequately accurate recovery from
buffer underrun condition/lossless linking. Not as accurate as DVD+RW,
but accurate enough for splices to be playable in virtually any
DVD-ROM/-Video unit. Yet! When it comes to DVD-R[W] recording you
apparently have to choose between
buffer underrun protection and
full DVD-ROM/-Video compatibility.
The latter is achieved only in Disc-at-once
recording mode and only if data-stream was maintained uninterrupted
throughout whole recording. Once again. Even though most vendors
implement lossless linking in DAO mode(*), full
DVD-ROM/-Video compatibility is achieved only if recording didn't
suffer from buffer underruns. The problem is that "offended"
sectors are denoted with certain linking chunk appearing as degraded
user data, few bytes, which are supposed to be "corrected
away" by ECC procedure(**). DVD+ splices are in turn
only few bits large and are "accounted" to sync patterns,
not to user data area. So that even if suffered from buffer
underrun, DVD+ sector is logically indistiguishable from DVD-ROM. Which
is why it's commonly referred to that DVD+RW/+R combine DVD-ROM/-Video
compatibility with [unconditional] buffer underrun protection.
As already mentioned, DVD+ groove has
"addressing information modulated into it," ADIP (ADress In
Pre-groove). This gives you an advantage of writing DVD+RW in truly
arbitrary order, even to virgin surface and practically instantly
(after ~40 seconds long initial format procedure). In addition, DVD+RW
can be conveniently written to with 2KB granularity(***).
DVD-RW in turn can only be overwritten in arbitrary order.
Meaning that it either has to be completely formatted first (it takes
an hour to format 1x media), or initially written to in a sequential
manner. And it should also be noted that block overwrite is
never an option if DVD-RW media was recorded in [compatible]
Disc-at-once or even Incremental mode, only whole disc blanking is.
Unlike DVD-R[W], DVD+R[W] recordings can be
suspended at any time without any side effects. Consider following
scenario. You have a lot of data coming in [at lower rate], which is to
be recorded into one file. Meanwhile it turns out that you have to
retrieve previously recorded data. This would naturally require
suspention of recording. Most notably in DVD-R [and naturally DVD-RW
Sequential] case it would result in a hole in the file being recorded.
So called linking area, most commonly 32KB gap, has to be introduced.
So that you either have to wait till the file is complete or figure out
how to deal with holey files. Thanks to ADIP, DVD+R recording is
resumed from the very point it was suspended at. In DVD-RW Restricted
Overwrite case no gaps are introduced, but if the media was formatted
only minimally, suspension/resuming procedure has to be applied and it
takes ~40 seconds to perform one. In DVD+RW case, suspension/resuming
is instant regardless media state.
What does all of the above mean in practice? Well, I
was actually hoping that readers would [be able to] figure it out by
themselves. Apparently a couple of "guiding" words are
needed... It means that it's trivial to employ DVD+RW for housing of
live and arbitrary file system, no special modifications to target file
system driver are required. Real-time VBR (Variable Bit Rate) Video
recordings are children's game.
Sometimes DVD+RW/+R recording strategy is referred
to as packet writing. I myself am reluctant to call it so (or
TAO/SAO/DAO) for the following reason. Despite the fact that DVD-R[W]
provides for lossless linking (within a packet/extent only),
packets/extents are still denoted with certain linking information
which distinguishes it (recording mode in question) from e.g.
Disc-at-once. Now the point is that written DVD+RW/+R media, rather its
Data Zone, does not contain any linking information and is
logically indistinguishable from one written in DVD-R[W] Disc-at-once
mode (or DVD-ROM for that matter).
It's maintained that signal from DVD+ groove (the
one essential for recording, not reading) is much stronger, which makes
it quite resistant to dust, scratches, etc.
According to Mt. Fuji draft
buffer underrun protection is not even an option in DVD-R DAO. It's
defined in Incremental Sequential mode and DVD-RW context. By the way,
note that this draft also discusses DVD+RW. You should be aware that
they refer to abandoned version which has very little to do with
DVD+RW/+R implementation being discussed here.
ECC redundancy does permit for more degradation,
more that this linking chunk that is, so that it hadly affects the
DVD "native" block size is 32KB, and 2KB
granularity is nothing but a trick, but you're excused from playing it,
i.e. reading 32KB, replacing corresponding 2KB and writing 32KB